Among the few buildings still extant within the Purana-Qila is the 'Qal'a-i-Kuhna-Masjid' (mosque of the Old Fort), built by Sher Shah in 1541. Its prayer-hall measures 51.20m by 14.90m, and is fronted by five openings with horseshoe-shaped arches. Narrow fluted pilasters flank the central arch, higher than the others and framed within a projection.
The recessed surface of the arch, through which there is an opening, is beautifully decorated with inlay of marble and other stones and contains a small oriel window at its apex. The two arches on either side are similarly treated but with less of ornamentation. In the arches at the ends plain grey stone is used instead of the red stone.
The minhrabs inside the hall are richly decorated with concentric arches, which enhance the scope for ornamentation. The rear-corners rise with double-storeyed towers and oriel windows. From both the ends in the hall staircases lead to a narrow passage on the second storey running right round the rectangular hall. The central Bay of the hall is surmounted by a beautiful dome, with traces of chhatris on either side. In the courtyard originally existed a shallow tank provided with a fountain.
This mosque occupies an important position in the development of the mosque, exemplifying the transition from the Lodi to Mughal styles. The façade of five arches, oriel windows and corner-towers at the rear are features, which have developed from the earlier mosques such as the Bara-Gumbad-Masjid, Moth-ki-Masjid and Jamali-Kamali-Masjid.

Sher-Mandal: To the south of the Qal'a-i-Kuhna-Masjid is a double-storeyed octagonal tower of red sandstone relived by marble. An octagonal pavilion or chhatri surmounts it. On each of its sides is a recessed arch in the centre. On the second storey the central chamber is cruciform, with recesses on its four sides. The dados of its interior are decorated with glazed tiles, while the upper portion contains incised and painted plasterwork.
The purpose of the building is not very certain. Sher Shah as a pleasure resort, but is believed to have been used as a library by Humayun may have built it, from the steps of which he fell down and ultimately met his end.

A Sound And Light Show At Purana Qila: This is the story of the city of cities… DELHI; of the site where a great empire rose and fell before the dawn of history; where citadels of emperors appeared and disappeared; a city of mysterious eternity whose old ruins proclaim a majestic and imperial past and whose present pulsates vibrantly with the even flowing life force of India.
The eternal Yamuna bears witness to the glorious and tumultuous 5,000-year-old history of Delhi. A history, which begins with the creation of Indraprastha by the Pandavas and the transformation of this barren gift of the Kauravas into an idyllic haven.
A history which encompasses the various kings and emperors who fixed their royal citadels here - Indraprastha, Lal Kot, Qila Rai Pithora, Siri, Jahanpanah, Tughlakabad, Ferozabad, Dinapanah, Delhi Sher Shahi or then Shahjahanabad. But, combined and integrated into one, these 'new cities' have always been called Delhi and howsoever many names it may have acquired, Delhi has always been intrinsically identified with power and imperial sway.
The historic Purana Qila, which has stood witness to Delhi's rejuvenation, periods of anarchy, and the rise and fall of empires, is the venue for the spectacular sound and light show which brings alive the history of the capital. Amidst the tranquility of the splendidly panoramic environs of Purana Qila, select episodes from the annals of Delhi's historic and legendary past are brought to life.
The viewer is transported centuries back in time to witness Draupadi being reduced to a Dasi (maid servant) of Hastinapur, the gallant Prithviraj Chauhan galloping away with the beauteous Samyogita, Sher Shah Suri being blown to bits by a misfired cannon, the clash of a sword wielded by the legendary Razia Sultan, Humayun tragically tumbling down the steps of his library and Bahadur Shah Zafar surrendering to the British.
These and many more such episodes out of Delhi's 5,000-year-old saga can be relived during this evocative 62-minute Son et Lumiere. Advanced technology has made it possible to add special effects, which combine with the unique ambience to make this show a hauntingly unforgettable experience.

The Lake and Zoo: Close to the Old Fort is a lake, which has paddle-boating facility. This lake is surrounded by a garden with rows of trees and flower plants. Inside the fort too there is well grafted and maintained lawns, which add to the greenery in the fort.
Delhi's Zoological Park is adjacent to the Purana Qila.

Bhairon Mandir: Among other buildings outside the Purana Qila are two Hindu temples, which are dedicated to Bhaironji, an incarnation of Shiva, and the destroyer of the Hindu trinity of Gods. There is a story around that the temple or at least its core dates back to the time of Indraprastha.
Conclusion can be derived that the basis of the temple might be of that era, even though the building itself is not much old. The most amazing factor of this temple is that the reigning deity of this temple is not offered milk as is usual in Shiva temples, instead its given alcohol. There is, however, a regular temple here too called the "Dhudhiya Bhairon", where one can offer milk.

Khairu's -Manazil-Masjid: In front of the Purana-Qila on the other side of the Mathura road stands the Khairu'1-Manazil-Masjid ('the most auspicious of houses'), a rubble-built structure with five arched openings in its prayer-hall, double-storeyed cloisters and an imposing gateway of red sandstone on the east.
The central Bay of the prayer-hall is provided with a dome, the other bays being roofed with vaults. Originally the façade of the prayer-chamber was profusely decorated with enameled tiles and the double-storeyed corridors were used as a madrasa.
Over the central arch of the prayer-chamber is an inscription, from which we learn that Maham Anga built it, with the assistance of Shihab-ud-Din Ahmad Khan during the reign of Akbar.
The mosque was built in 1561. Maham Anga was one of the wet-nurses of Akbar and held considerable influence over him. Her son, Adham Khan was a nobleman and a general in Akbar's army, whose tomb is described elsewhere. Shihab-ud-Din Ahmad Khan was a relation and friend of Maham Anga and a powerful courtier, who held the position of the governor of Delhi at one time.